Polymer Composite Vacuum Components

ABSTRACT

A gauge having a housing formed of a polymer material and one or more electrical feedthrough pins disposed in the housing. The electrical feedthrough pins can be oriented substantially perpendicular to each other and have complex shapes.

RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.16/415,313, filed May 17, 2019, which is a continuation of U.S.application Ser. No. 14/994,969, filed Jan. 13, 2016, now U.S. Pat. No.10,359,332, issued Jul. 23, 2019, which claims the benefit of U.S.Provisional Application No. 62/103,968, filed on Jan. 15, 2015, and U.S.Provisional Application No. 62/191,140 filed on Jul. 10, 2015. Theentire teachings of the above applications are incorporated herein byreference.

BACKGROUND OF THE INVENTION

Accurate and repeatable pressure measurements are an importantrequirement for the operation of both industrial and research vacuumsystems. Pressure gauge sensors used to measure vacuum levels in suchapplications operate based on a wide range of technological principlesand share common building blocks in their design, including: (1) a leaktight envelope that houses the pressure sensing elements, (2) electricalfeedthroughs that bridge the envelope walls and exchange power, biasvoltages and measurement signals with the electronics and (3) a flangethat allows leak tight connection of the gauge sensor to the vacuumsystem port. Historically, pressure gauge sensors have relied onwell-established design and manufacturing methodologies that usemetallic materials and ceramic insulators. Legacy gauge constructionmaterials are the result of the natural evolution of vacuum technologyresearch and satisfy the mechanical, electrical and high vacuumcompatibility properties that are expected from vacuum pressure sensors.

Ionization vacuum gauges are well known and include both hot and coldcathode gauges. A cold cathode ionization gauge has a pair of electrodes(i.e., an anode pin and a cathode cage) in an evacuated envelope whichis connected to the vacuum to be measured. In the cold cathode gauge, ahigh DC voltage potential difference is applied between the anodeelectrode and the cathode electrode to cause a discharge current to flowtherebetween. A magnetic field is applied along the axis of theelectrodes in order to help maintain the discharge current at anequilibrium value which is a repeatable function of pressure. Coldcathode ionization gauges are used to measure pressures extending frommedium to high vacuum levels (e.g., in the range of 1E-10 to 1E-02Torr).

Accordingly, an ionization vacuum gauge provides an indirect measurementof vacuum system total pressure by first ionizing gas molecules andatoms inside its vacuum gauge envelope and then measuring the resultingion current. The measured ion current is directly related to the gasdensity and gas total pressure inside the gauge envelope, i.e., as thepressure inside the vacuum system decreases, the measured ion currentdecreases. Gas specific calibration curves provide the ability tocalculate total pressures based on ion current measurements.

SUMMARY OF THE INVENTION

Components in high performance vacuum systems have historically beenfabricated from stainless steel, which provides low outgassing and canbe machined into parts that can be subsequently joined together intoleak tight structures that house the pressure sensing elements andprovide electrical access to the internal components. One disadvantageof stainless steel components is that unique geometries are difficult tomanufacture due to the limits by which parts can be machined. Typically,the housing is machined to the appropriate geometry by removing metalfrom a starting product. Feedthrough connectors are created through acombination of ceramic insulators and conductive metallic pins that areassembled together through a series of welding and brazing operations.It is challenging to manufacture a housing that has nonlinear electricalfeedthrough pins with traditional machining processes for metalcomponents. Additionally, stainless steel can be relatively expensive,thereby increasing the cost of manufacturing for all high vacuumcompatible pressure measurement gauges. Another disadvantage ofstainless steel components is the requirement to produce leak tightseals compatible with standard vacuum flanges, which are expensive andvery time consuming to implement. Plastic materials provide anopportunity to develop alternative sealing techniques, compatible withtraditional sealing flanges, that are cheaper, have lower manufacturercost, and provide faster installation. Plastics do not only offer thepromise of cheaper pressure gauging products for the vacuum industry,but also an opportunity to significantly improve the workflow for vacuumpractitioners. When a process chamber is opened to the atmosphere for anoperational reason, the sensor can quickly and inexpensively be switchedwith a new one, thereby eliminating the need to take manufacturingoffline due to a faulty gauge that is past its useful lifetime.Additionally, plastic materials offer an opportunity to provide designsthat would be inconceivable with metal and ceramic components.

Described herein are methods of forming components of a gauge, forexample an ionization gauge, from polymers. The use of polymers candecrease manufacturing costs by permitting the use of molds to rapidlyform components of the required geometry. Additionally, a molded housingcan have electrical feedthrough pins passing directly through theinsulating housing at unique geometries and angles that are difficult tomanufacture when the housing is formed of stainless steel or anothermetal. Additionally, feedthrough pins can be designed that have longerpath lengths through the housing, which can improve the quality of thevacuum by decreasing the flux of gas leaking into the vacuum space.

Described herein is a gauge, such as an ionization gauge, having ahousing formed of a polymer material and an electrical feedthrough pindisposed through the housing.

Also described herein is a method of making a housing for use in agauge, such as an ionization gauge. The method can include positioningan electrical feedthrough pin in a mold, flowing molten polymer into themold, and allowing the molten polymer to solidify to form a housing. Themethod can further include coating an interior side surface of thehousing with a vacuum sealing material. The mold can form a flange tocouple the gauge to a process chamber.

A second electrical feedthrough pin can be disposed through the housing.One electrical feedthrough pin can be disposed through a base of thehousing and the second electrical feedthrough pin can be disposedthrough a side of the housing. The electrical feedthrough pins can beoriented substantially perpendicular to each other. The electricalfeedthrough pin can have a nonlinear portion, which can be disposedthrough the polymer material of the housing. The electrical feedthroughpin can be coupled to an anode or a cathode.

The electrical feedthrough pin can have a threaded portion disposedwithin the polymer of the housing. The electrical feedthrough pin can befurther coupled to the housing with an O-ring. The electricalfeedthrough pin can have an extended disc portion disposed within thepolymer of the housing. The electrical feedthrough pin can be formed bymolding a conductive polymer into the sensor housing between twoelectrical feethrough pins, thereby coupling two conductors with aconductive matrix embedded within the housing.

The electrical feedthrough pin can be further coupled to the housingwith a component having a knife edge. The component having a knife edgecan be formed of a shape memory polymer, preferably athermally-activated shape memory polymer.

The gauge can further include a sensor disposed within the housing. Thesensor can be, for example, the inverted magnetron electrode structureof a cold cathode ionization gauge. An interior side surface of thehousing can be coated with a vacuum sealing material. A flange cancouple the gauge to a process chamber. The flange can be integrallymolded to the housing in a monolithic envelope-flange design.

Described herein is a component, such as a closure, of a high vacuumhousing. The component can include a molded polymer with avacuum-sealing coating on a vacuum side. The component can be a vacuumblank. The vacuum blank can have a knife edge or other raised structure.The molded polymer can be a shape memory polymer, preferably athermally-activated shape memory polymer. The component can include aknife edge or other raised structure.

Also described herein is a method of sealing a high vacuum housing. Themethod includes inserting a molded polymer having a vacuum-sealingcoating on the vacuum side into an orifice, removing the molded polymerfrom the orifice, and heating the molded polymer to restore the moldedpolymer to a pre-deformed shape. The molded polymer can be a shapememory polymer that deforms upon insertion into the orifice.

Also described herein is a gauge, for example, a cold cathode ionizationgauge. The gauge can include a cylindrical cathode cage having a base,which can have an opening, a cathode pin electrically coupled to thecathode, an anode disposed through the opening of the base. a polymerhousing surrounding the cylindrical cathode cage, and an insulator atthe base of the cylindrical cathode cage that protects the polymerhousing at an interface between the cylindrical cathode cage and thepolymer housing. The gauge can include a sputter shield disposed withinthe cylindrical cathode cage that is coaxial with the anode. The gaugecan include a starter that is electrically coupled to the anode anddisposed within the cylindrical cathode cage. A bottom face of the baseof the cylindrical cathode cage can have a lip surrounding theinsulator. An upper portion of the cold cathode cage can have a lip thatextends radially outward from the cold cathode cage into the polymerhousing. The gauge can include a ferromagnetic screen coupled to anupper portion of the cold cathode cage. The opening of the base of thecylindrical cathode cage can have a step edge to shadow the insulator.The polymer housing can include a flange to couple the ionization gaugeto a chamber. A cylindrical magnet can surround at least a portion ofthe polymer housing. An O-ring can be disposed around the anode, withinthe polymer housing, and below the base of the cylindrical cathode cage.The gauge can include a printed circuit board, wherein the anode isdisposed through the printed circuit board and the polymer housing ismechanically coupled to the printed circuit board. The polymer housingcan be formed of polyether ether ketone (PEEK), polypropylene, orpolycarbonate. The polymer housing is formed of a polymer having anoutgassing rate less than 5×10⁻⁶ Torr L s⁻¹ cm⁻². The polymer housingcan be formed of a polymer that is not hygroscopic. The gauge caninclude a cylindrical insulator that surrounds a portion of the anodedisposed through the printed circuit board. The gauge can include anenclosure, which can be formed of polymer, that at least partiallysurrounds the polymer housing and printed circuit board. The gauge caninclude a connector coupled to the enclosure.

Also described herein is an assembly for a gauge, which can include acylindrical cathode cage having a base, which can have an opening, acathode pin electrically coupled to the cathode, an anode disposedthrough the opening of the base, and an insulator at the base of thecylindrical cathode cage that is configured to protect a polymer housingat an interface between the cylindrical cathode cage and the polymerhousing. The assembly is configured for insertion into a mold, typicallyfor use in making a gauge. The gauge assembly can include a sputtershield disposed within the cylindrical cathode cage that is coaxial withthe anode. The gauge assembly can include a starter that is electricallycoupled to the anode and disposed within the cylindrical cathode cage. Abottom face of the base of the cylindrical cathode cage can have a lipsurrounding the insulator. An upper portion of the cold cathode cage canhave a lip that extends radially outward from the cold cathode cage intothe polymer housing. The gauge assembly can include a ferromagneticscreen coupled to an upper portion of the cold cathode cage. The openingof the base of the cylindrical cathode cage can have a step edge toshadow the insulator.

Also described herein is a method of making a gauge. The method caninclude positioning within a mold a gauge assembly, such as described inthe preceding paragraph, flowing molten polymer into the mold, andallowing the molten polymer to solidify to form a housing around thecylindrical cathode cage, cathode pin, anode, and insulator. The methodcan include positioning a cylindrical magnet surrounding at least aportion of the polymer housing. The method can include positioning anO-ring around the anode, within the polymer housing, and below the baseof the cylindrical cathode cage. The method can include mechanicallycoupling a printed circuit board to the polymer housing, wherein theanode is disposed through the printed circuit board. The polymer housingcan be formed of polyether ether ketone (PEEK), polypropylene, orpolycarbonate. The polymer housing can be formed of a polymer having anoutgassing rate less than 5×10⁻⁶ Torr L s⁻¹ cm⁻². The polymer housingcan be formed of a polymer that is not hygroscopic. The method caninclude positioning a cylindrical insulator that surrounds a portion ofthe anode disposed through the printed circuit board. The methodpositioning an enclosure that at least partially surrounds the polymerhousing and printed circuit board. The enclosure can be formed of apolymer. The method can include coupling a connector to the enclosure.

Also described herein is a closure for a vacuum housing formedsubstantially of polymer. The closure can be metal-coated. The closurecan also have a knife edge, such as in a CONFLAT flange.

The components and methods described herein can provide a number ofadvantages and are applicable to a variety of components in vacuuminstrumentation, including Convection Enhanced Pirani (CEP) gauges,Micro-Ion sensors, ion trap sensors, metal Bayard-Alpert sensors (suchas the STABIL-ION sensor from MKS Instruments, Inc., Andover, Mass.,USA), glass Bayard-Alpert sensors, and thermocouple sensors.Additionally, the injection molding process is very reproducible, and agauge produced by injection molding could be shipped directly from aninjection molding facility to an end user.

Distinct components of a vacuum gauge can be consolidated into onemolded or machined polymer structure, thereby reducing the number ofassembly and joining steps required to construct the sensor. In otherwords, the components and methods described herein provide for simplerdesigns that can be more cost-effective to manufacture. One particularexample is a gauge, such as an ionization gauge having a housing with aflange and metal feedthrough pins, that is created in one injectionmolding step. As an alternative, the feedthrough pins can be simplypress-fit after an injection molding process.

Unique geometries can be manufactured, such as nonlinear electricalfeedthrough pins, which are difficult to construct using traditionalmachining processes based on metallic materials. In some embodiments,cost-prohibitive materials can be coated in thin layers for tailoredapplications, such as harsh environments (e.g., implant or chemicaletch). New sealing components with low outgassing, due to the compliantnature of the polymers, can be constructed. Vacuum feedthroughs can beconstructed by press-fitting electrical conductors, gas flow pipes, orother mechanical structures through polymer sealing components.Alternatively, polymer can be injection molded around those components,thereby eliminating the need to press-fit them. The vacuum feedthroughscan be constructed so that a separate glass, metal, or ceramic sealingcomponent is unnecessary. In other words, the components can beconstructed without having a separate vacuum-sealing structure otherthan the interface between the polymer and the vacuum feedthrough pin.Vacuum feedthroughs can also be constructed by including inserts,whether metal or another material, in the polymer molding process tocreate a composite structure comprised of both electrical and/ormechanical feedthrough and the supporting structure itself. Anotheradvantage of polymer molding is that the conductive structures, such asthe cathode and the electrical feedthrough, can be pre-joined by weldingor other means when they are easier to manipulate, and then the envelopeand flanges can be molded around them.

More recently there has been increased interest from the vacuum industryto produce lighter, smaller and lower cost pressure gauging products.Vacuum products present their own challenges for compatibility withoperation at, or exposure to, high vacuum. Alternative constructionmaterials, such as polymeric plastics, are identified herein to producea new generation of pressure measurement gauges that are compatible withoperation at, or exposure to, high vacuum levels and can provide therequired pressure measurement performance at a reduced cost and in alighter, smaller and even disposable package.

The present work describes the selection of the proper materials andmanufacturing methodologies that will allow to replace all buildingblocks for gauge manufacturing with alternative designs that includeplastics (low cost material) as the main manufacturing components. Thegoal is to produce a new generation of plastic gauges which measurepressure by a variety of technologies, including (but not restrictedto): ionization, thermal conductivity, friction and diaphragmdeflection. With proper material selection, a new generation of plasticvacuum gauges, compatible with operation in high vacuum systems, willbecome standard in the vacuum industry.

Plastic materials and plastic manufacturing techniques can be used todesign and manufacture the typical building blocks of all high vacuumcompatible pressure gauges, including: leak tight housing, electricalfeedthroughs and mounting flanges. The cold cathode ionization gauge isused as an example of a high vacuum compatible gauge that can bedesigned using plastic materials and it is clear that similar conceptscan be used to design other vacuum compatible gauges that share commonbuilding blocks. Examples include: hot cathode gauges, pirani gauges andeven diaphragm gauges. The development of a plastic vacuum gaugerequires many different technical considerations including: propermaterial (or materials) selection, cost effective and high vacuumcompatible assembly/sealing techniques, protection of exposed plasticsurfaces from hazardous environmental conditions including reactiveprocess gases and internally generated species (such as ions andmetastables in internal plasmas). The design and manufacture of plasticgauges is one path to the development of low cost gauges. Plastics donot only offer low cost material alternatives but also the ability toreduce the number of assembly steps leading to reduced assembly errorsand cost.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing will be apparent from the following more particulardescription of example embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingembodiments of the present invention.

FIG. 1A is an illustration of a housing for an ionization gauge. Thehousing has two electrical feedthrough pins that are axially disposedthrough the base of the housing.

FIG. 1B is an illustration of a housing for an ionization gauge. Thehousing has one electrical feedthrough pin axially disposed through thebase and a second electrical feedthrough pin disposed through the sideof the housing.

FIG. 1C is an illustration of a housing for an ionization gauge. Thehousing has one electrical feedthrough pin axially disposed through thebase and a second electrical feedthrough pin disposed through the baseof the housing. The second electrical feedthrough pin is nonlinear andmakes a 90 degree turn.

FIG. 1D is an illustration of a housing for an ionization gauge. Thehousing has one electrical feedthrough pin axially disposed through thebase and a second electrical feedthrough pin disposed through the sideof the housing. The second electrical feedthrough pin is nonlinear andcurves as it passes through the housing.

FIG. 1E is an illustration of a polymer housing having a helicalelectrical feedthrough pin.

FIG. 1F is an illustration of a polymer housing having non-axialelectrical pins.

FIG. 2 is an illustration of an electrical feedthrough pin disposedthrough the housing of an ionization vacuum gauge. The electricalfeedthrough pin has a threaded portion disposed within the polymer ofthe housing.

FIG. 3 is an illustration of an electrical feedthrough pin disposedthrough the housing of an ionization gauge. The electrical feedthroughpin is further coupled to the housing with an O-ring.

FIG. 4 is an illustration of an electrical feedthrough pin disposedthrough the housing of an ionization gauge. The electrical feedthroughpin is further coupled to the housing with a shape memory polymer havinga knife edge.

FIG. 5 is an illustration of an electrical feedthrough pin disposedthrough the housing of an ionization gauge. The electrical feedthroughpin has an extended disc portion disposed within the polymer of thehousing.

FIG. 6 is an illustration of a sensor disposed within the housing of anionization gauge.

FIG. 7 is an illustration of a vacuum blank formed of a polymer.

FIG. 8 is an illustration of a component of a high vacuum blank that hasa knife edge.

FIG. 9 is an illustration of an electrical feedthrough pin formed fromtwo metal conductors and an embedded conductive material.

FIG. 10 is a cross-sectional view of one embodiment of a polymercomposite cold cathode gauge.

FIG. 11 is three-dimensional cross-sectional view of one embodiment of apolymer composite cold cathode gauge.

FIG. 12 is a magnified view of one embodiment of a polymer compositecold cathode gauge.

FIG. 13 is a cross-sectional view of another embodiment of a polymercomposite cold cathode gauge.

FIG. 14 is a cross-sectional view of an embodiment of a polymercomposite cold cathode gauge having a magnet insert molded into thesensor.

FIG. 15 is a cross-sectional view of yet another embodiment of a polymercomposite cold cathode gauge having an extended cathode cage.

FIGS. 16A-C are illustrations of polymer molded flanges. FIG. 16A is astandard flange. FIG. 16B is an insert molded centering ring. FIG. 16Cis a one piece flange and centering ring.

FIGS. 17A and 17B are illustrations of an injection molding process.FIG. 17A is an illustration of an assembly for a gauge prior toinjection molding, and FIG. 17B is an illustration of the gauge afterinjection molding.

DETAILED DESCRIPTION OF THE INVENTION

A description of example embodiments of the invention follows.

The cold cathode ionization vacuum gauge described herein relies on theinverted magnetron principle. The gauge is of cylindrical symmetry. Alarge voltage potential difference (i.e., radial electric field) betweenthe anode pin, located on the axis of the gauge, and the cylindricalcathode, inside the vacuum envelope, provides energy to the electronsfor the ionization events to occur. A crossed axial magnetic fieldprovides the longer electron trajectory path length required to sustaina discharge inside the envelope. The discharge current is the measuredquantity and is proportional to the total pressure in the system.

The discharge is established through an avalanche ionization processthat generally starts with a single electron being released into theionization volume of the gauge. The process is responsible for releasingan electron can include a field emission event or a cosmic rayionization process. The avalanche process relies on the long path lengthfor the electron trajectories that leads to many ionization processesper electron. Each ionization process releases an ion as well as anadditional electron that is added into the discharge. As the ionscollide with the cathode internal walls, additional electrons are alsoreleased into the discharge, thereby contributing to the total charge.The electrical discharge current flowing from anode to cathode(consisting of ions and electrons) reaches a value that is proportionalto the pressure in the system.

The cold cathode ionization vacuum gauge described herein is an invertedmagnetron design. The inverted magnetron design, shown in FIG. 1A-F ofthis application, includes a magnet assembly 180 and 185. The conceptsdescribed herein are equally applicable to a Penning type design.

FIGS. 1A-1F illustrate embodiments of a housing for an ionization gauge100. A housing 110 a-d is formed of a polymeric material and anelectrical feedthrough pin 120 is disposed through the housing 110 a-f.The electrical feedthrough pin 120 can be coupled to an anode 122.Alternatively, the tip portion 122 of the electrical feedthrough pin 120located within the interior of the housing 110 a-f can function as ananode. A cylindrical cathode 130 is located within the interior of thehousing 110 a-f. In some embodiments, the cylindrical cathode 130 can becoated directly on the polymer on the vacuum side of the envelope.Common coating methods can be used to deposit the cathode. Depending onthe final coating material, electroless plating followed byelectroplating can be used as well as direct deposition methods, such asPhysical Vapor Deposition (PVD), Chemical Vapor Deposition (CVD), orPlasma Enhanced Chemical Vapor Deposition (PECVD). When designing thiscoating, consideration should be given to the fact that the ions makingup the plasma in a cold cathode sensor will sputter material from thecathode as they collide with it. Up to one gram of material can besputtered off the cathode walls throughout the life of the gauge. Thecoating material should therefore have a thickness of >0.010 inches. Thecoating material should also ideally have a low sputtering rate and notcontain any elements with ferromagnetic properties. A material such astitanium or aluminum can be used. In some embodiments, the cylindricalcathode 130 can be incorporated into the polymer housing 110 a-f bypress fitting, heating then press fitting, press fitting then heating,threading, threading and heating, heating and threading, or moldingdirectly in place.

In some embodiments, a second electrical feedthrough pin 140 a-f can bedisposed through the housing 110 a-d. In the embodiment of FIG. 1A, thesecond electrical feedthrough pin 140 a is collinear with the firstelectrical feedthrough pin 120 and electrically coupled to the cathode130. In the embodiment of FIG. 1B, the second electrical feedthrough pin140 b is oriented perpendicular to the first electrical feedthrough pin120. In the embodiment of FIG. 1C, the second electrical feedthrough pin140 c is nonlinear and makes a 90 degree turn so that it is disposedthrough the base of the housing. In the embodiment of FIG. 1D, thesecond electrical feedthrough pin 140 d is nonlinear and makes a 90degree turn so that it passes through the side of the housing 110 d.

Since the housing 110 a-f is formed of a polymer material, the housingcan be manufactured by a rapid throughput molding process. Additionally,the electrical feedthrough pins 120 and 140 a-f can be oriented atunique positions prior to forming the housing. Then, the polymer housingcan be formed around the electrical feedthrough pins 120 and 140 a-fAdditionally, the electrical feedthrough pins can have complex,nonlinear geometries, as illustrated by electrical feedthrough pins 110c-d. Nonlinear geometries can include a wide variety of shapes. Forexample, nonlinear geometries can include changes in the direction ofthe longitudinal axis of an electrical feedthrough pin. Nonlineargeometries can also include changes in the plane in which the pin isoriented. For example, the electrical feedthrough pins 140 a-f can becurved, and can have a curved portion disposed through the polymermaterial of the housing 110 a-f. Notably, the molding process can permitthe construction of a housing having electrical feedthrough pins 120 and140 a-f that access locations within the interior of the housing 110 a-fthat are inaccessible or difficult to access when the housing is formedof a metal, such as stainless steel. Another example of a nonlinearelectrical feedthrough pin is illustrated in FIG. 1E, which has ahelical electrical feedthrough pin 121. Another example of a nonlinearelectrical feedthrough pin is illustrated in FIG. 1F, which has a curvedfeedthrough pin 140 f Increasing both the length and tortuosity, oramount of curvature, of feedthrough pins increases the path length thatatoms or molecules of gas must traverse in order to pass from an airside of the gauge into a vacuum sealed area. Therefore, increasing thelength and tortuosity of feedthrough pins decreases the flux of gas intothe vacuum, thereby improving vacuum quality and increasing theprecision and accuracy of gauge measurements. These types of designshave historically been difficult to manufacture using stainless steelcomponents.

The housing 110 a-f can also include a flange portion 150, which can beintegrally molded with the housing 110 a-f. The flange portion 150 cancouple the ionization gauge to a process chamber. This flange portioncan incorporate a gasket molded into the polymer, or a centering ringthat holds the O-ring in a Klein Flange, or KWIK FLANGE type seal. Inthe case where the gasket is incorporated directly into the flange, ametallic knife edge on the chamber can deform the seal or the polymerflange forming a vacuum seal between the polymer and the metal knifeedge. One particular advantage of polymer molded vacuum components isthat a housing having a flange and metal feedthrough pins disposedthrough the housing can be formed in a single manufacturing step, ratherthan separately manufacturing three distinct components that aresubsequently joined together. Another particular advantage of using apolymer housing 110 a-f is that a centering ring can be designed as anintegral component of the flange. The centering ring can be moldeddirectly into the flange portion 150 of the polymer housing 110 a-f. Apolymer housing can be formed having other flange types as well. Asillustrated in FIGS. 16A-C, a housing can be formed having a standardflange (FIG. 16A), an insert molded centering ring (FIG. 16B), or a onepiece flange and centering ring (FIG. 16C).

The electrical feedthrough pins can have a number of unique geometries,particularly where the electrical feedthrough pin passes through thepolymeric housing material. FIGS. 2-5 illustrate electrical feedthroughpins disposed through the housing of a gauge. The housing 115 having avacuum side 127 and an exterior side 128 (sometimes referred to as the“air” side) is formed of a polymeric material. In FIGS. 2-4, theelectrical feedthrough pin 125 a-c has a threaded portion 145 a-cdisposed within the polymer of the housing 115. In FIG. 3, theelectrical feedthrough pin 125 b is further coupled to the housing withan O-ring 155. The threaded portion 145 a-c increases the surfacecontact area between the electrical feedthrough pin 125 a-c and polymer115, thereby increasing the path length that an atom or molecule musttraverse to diffuse from the high-pressure side (e.g., the exteriorside) to the vacuum side (e.g., the interior side) of the electricalfeedthrough pin 125 a-c. The O-ring 155 further seals the interfacebetween the electrical feedthrough pin 125 b and the polymer material ofthe housing 115. In FIG. 4, the electrical feedthrough pin 125 c isfurther coupled to the housing with a component 190 having a knife edgeportion 195, which facilitates coupling to the housing 115. Thecomponent 190 can be formed of a shape memory polymer, such as athermally-activated shape memory polymer.

The use of molding techniques enables the fabrication of other complexstructures having long path lengths between the exterior (atmospheric)side and the interior (vacuum) side of the electrical feedthrough pin.FIG. 5 illustrates another electrical feedthrough pin 125 d disposedthrough the housing 115 of an ionization gauge. The electricalfeedthrough pin 125 d has an extended disc portion 160 disposed withinthe polymer of the housing 115 and an extended disc portion 165 on theexterior side of the housing115. Similar to the threaded feedthrough,the extended disc increases the surface contact area between theelectrical feedthrough pin 125 d and polymer 115, thereby increasing thepath length that an atom or molecule must traverse to diffuse from thehigh-pressure side (e.g., the exterior side) to the vacuum side (e.g.,the interior side) of the electrical feedthrough pin 125 d. More complexstructures, such as multiple discs or combinations of threaded portionsand discs, can also be used.

The techniques described herein can also be used on existing vacuumheaders or assemblies. Vacuum sensors can be purchased from supplierspre-packaged into standard vacuum compatible headers such as T05 andT08, which are inexpensive, common, readily available standardelectrical headers. These sensors are often integrated into a largervacuum gauging solution containing multiple sensors as required toprovide enhanced pressure ranges. A method is needed to seal theseheaders into the larger vacuum gauge and the techniques described abovecan be used for this application as well. FIG. 6 is an illustration of asensor 170 disposed within the housing of an ionization vacuum gauge.

The selection criteria for materials for the housing includes severaldifferent attributes: First, the material should produce minimaloutgassing. This includes low outgassing of materials adsorbed on theinternal surfaces exposed to vacuum as well as reduced outgassing ofplasticizers from the bulk of the material. Polymers providing anoutgassing rate less than 5×10⁻⁶ Torr L s^(—1) cm⁻² are preferred asthey provide the ability to develop vacuum gauges capable of measuringpressures and/or operating at pressures as low as 1E-08 Torr withtypical pumping systems. For comparison, outgassing rates for componentsof construction are listed in Table 1. Second, the material should havea low gas permeation rate from the air side/exterior side to the vacuumside. The permeation rate is regulated through a combination of wallthickness and polymer composition. Third, the material selected shouldbe compatible with the manufacturing processes selected to design thegauge. Particularly important are thermal properties of materials andchemical compatibility: the plastic materials selected must becompatible with chemical compounds present in the vacuum processesmeasured by the gauge. Additionally, polymers that are not hygroscopic,or those having a lower hygroscopicity, are preferred. Suitablepolymeric materials for the housing (110 a-f; 1030) include thermosetplastics and thermoplastics.

TABLE 1 Outgassing rates Outgassing rate Component (Torr L s⁻¹ cm⁻²)Stainless steel  2.5 × 10⁻⁹ Polypropylene 7.73 × 10⁻⁷ Polyether etherketone (PEEK) 2.44 × 10⁻⁶ High density polyethylene (HDPE) 2.68 × 10⁻⁶Polycarbonate (PC) 3.04 × 10⁻⁶

Particular polymer materials that are suitable include polyether etherketone (PEEK), polyolefins (e.g., polypropylene), polymethylmethacrylate (PMMA), acrylonitrile butadiene styrene (ABS),fluoropolymers, polytetrafluoroethylene, polyethylene, NALGENE, VESPELpolyimide, polycarbonates, polystyrene, and KAPTON. Some polymers, suchas PEEK, have shape memory properties, particularly when exposed toheat. These properties can be exploited to enhance the integrity of thecomponents or make them more easily reusable.

One particularly suitable polymer is polyether ether ketone (PEEK),which is not hygroscopic and provides low oxygen and water permeation,low outgassing, and sufficiently high tensile strength and flexuralmodulus. Another suitable polymer is polycarbonate, which provides highdielectric strength (and, therefore, low leakage current between theelectrodes), low outgassing, and is metal-coatable. Polyolefins, such aspolypropylene, are also suitable. In particular, polypropylene is nothygroscopic and provides low water absorption, low outgassing, highdielectric strength, and quick pressure pump down. In operation, most ofthe flux into the vacuum system is due to water molecules, which tend toform monolayers on the steel surfaces. However, polypropylene and otherpolyolefins have a lower affinity to water compared to other polymers,thus reducing the quantity of water that may need to be pumped out of avacuum system. In ultra-high vacuum systems, even a small quantity ofwater molecules can significantly impact the quality of the vacuum, andtherefore reducing the affinity of the material to water adsorption cansignificantly reduce operating burdens on the user. Using polymers withlow water affinity offers the opportunity to produce fast pump-downs asit is not necessary to remove layers of water from the walls to achieveultimate vacuum. In summary, material selection for a gauge housing is amultivariable process that involves considering the affinity of thematerial to water, its permeability to atmospheric gases, and itsability to be formed to the desired shape using low cost manufacturingprocesses.

The housing can be fabricated by known polymer molding techniques.Typically, one or more electrical feedthrough pins are positioned in amold. Molten polymer is flowed into the mold and allowed to solidify toform a housing. This construction technique allows for virtually anyshape conductive material to be used, such as square, or diamond shape,to accommodate keying of connectors or otherwise allowing for a uniquedetermination of conductor geometries. It also allows the conductor tofollow a nonlinear path through the polymer from the atmospheric (air)side of the gauge to the vacuum side. These non-straight paths may beuseful, for example, in spatially controlling the location of magneticfields generated by the currents flowing in the wire, or allowing thefeedthrough to route around shielding or other barriers to deliver theelectrical signal where it is needed in the gauge.

Alternatively, press-fit electrical feedthrough pins or tubes can beplaced into holes molded into the body of the housing after the polymerhas solidified. Typically, the holes drilled in the plastic are slightlysmaller than the electrical feedthrough pins that carry the signal. Theelectrical feedthrough pins can be press fit into the holes forming atight seal between the polymer and the rods. Specifically, in oneparticular example, the holes can be 0.0425 inches and the electricalfeedthrough pins can be made of stainless steel 0.0575 inches indiameter. One advantage of this approach is that the electricalfeedthroughs do not need to be parallel to the axial direction of thegauge, as is common for most vacuum feedthroughs built using ceramics asthe insulator. Other pertinent manufacturing techniques are injectionmolding, insert molding, blow molding, and three dimensional printing.In addition to pressing fitting feedthroughs, FIGS. 2-4 show that it isalso possible to screw threaded feedthroughs into a housing. The threadsprovide a press fit to the housing, and a more torturous path for gasmolecules to leak from the air side to the vacuum side of the housing.

In the embodiments described herein, the housing is made out of a singlematerial. In some vacuum instruments, different portions of the housingor gauge may have different design requirements, such as requirementsfor thermal properties, conductivity, permeation or outgassing. In orderto satisfy these different requirements, different polymers can be usedto fabricate different sections of the housing or gauge. These portionscan then be bonded together using traditional means, such as adhesives.Additionally, a metallic or other barrier coating protecting and/orlimiting outgassing from the interface can be formed on one or moresurfaces of the housing. If the materials are compatible, the bond canbe formed by melting or otherwise causing one of materials to flow, andthen joining a first portion of the housing to a second portion of thehousing before it re-polymerizes or hardens. The electrical feedthroughpin can be made of many different types of conductive material, withoutneeding to account for its high-temperature performance and coefficientof expansion compared to the ceramic or glass seals. Another advantageto this type of feedthrough is that it will accommodate virtually anytype of conductive material, without needing to account for itshigh-temperature performance and coefficient of expansion compared toceramic or glass seals. The conductive material, for example, can be aconductive carbon fiber, silver doped or silver impregnated elastomers,or other known conductors. Legacy feedthroughs generally require the useof brazing materials to bond metal to ceramics, and such brazingmaterials can be incompatible with customer applications. Brazing istypically not required for the polymeric gauges described herein.

In order to eliminate the need for a metal to plastic seal, FIG. 9illustrates an electrical feedthrough pin 300 constructed of twoconductors 310 and 320 sandwiching a conductive polymer matrix 330. Oneof the conductors (e.g., 310) is positioned on the vacuum side (e.g.,interior) of a sensor housing 315 and the other conductor (e.g., 320) ispositioned on the atmospheric side (e.g., exterior) of a sensor housing315. In this configuration, the conductive polymer matrix 330 can bemolded directly into the sensor housing 315 in the case ofthermoplastics or using insertion molding when this technique is notpossible. The conductive polymer matrix 330 electrically couples the twoconductors 310 and 320. Several suitable polymers are known in theindustry including: poly(pyrrole)s (PPY), polyanilines (PANT),poly(thiophene)s (PT), poly(3,4-ethylenedioxythiophene) (PEDOT),poly(p-phenylene sulfide) (PPS), poly(acetylene)s (PAC) andpoly(p-phenylene vinylene) (PPV).

Several techniques can be used to improve the vacuum seal of such afeedthrough. One approach is to add a vacuum compatible adhesive, suchas TORR SEAL, VACSEAL, or LOCTITE, to the pin or in the drilled hole.The adhesive will increase the bond strength between the polymer and theelectrical feedthrough pin resulting in an increase in both mechanicalstrength and the vacuum seal. A disadvantage of using adhesives is thatmany of them can outgas under vacuum unless some type of vapor barriercoating, as described above, is applied to the vacuum side of theelectrical feedthrough pin. Electrical feedthrough pins, particularlythose having a threaded portion, can be further sealed with an inertmaterial, such as TEFLON tape.

Several other steps can be taken to increase both the vacuum performanceof the seal and its mechanical strength. The application of heat cancause the plastic to soften and flow further increasing the contactsurface between the conductor and polymer. Heat can be applied inseveral different ways. The polymer itself can be heated to soften thematerial allowing the hole to be further undersized in a press fitoperation. Alternatively, the conductive material can be ohmicallyheated after the press fit to cause the plastic to flow increasing theintegrity of the seal.

In another embodiment, a component of a high vacuum housing is a moldedpolymer with a vacuum-sealing coating on the vacuum side of the housing.One particular embodiment is shown in FIG. 7, which is an illustrationof an O-ring sealed (NW25KF) vacuum blank, which is a common vacuum typeconnection that uses an O-ring mounted on a metallic centering ringplaced between smooth surfaces to form a face seal. A clamp is used tohold the O-ring and vacuum components together. An example vacuum blankhas been formed from the polymer PEEK, and another example vacuum blankhas been formed from the polymer acrylonitrile butadiene styrene (ABS).These blanks can be electroless plated with copper, and subsequentlyelectroplated with nickel. Blanks are used to cover ports in the chamberthat are currently not in use. Traditionally, ports are disks made ofstainless steel or another metallic material that have a knife edge,groove, or other structure machined onto the chamber side thatfacilitates sealing to a gasket. These are generally smooth on thenon-chamber side. By injection molding the structure of the blank, theblank can be produced in large volumes, at high rates and low cost, andthe mechanical structure of the blank can be combined with the sealingstructure of the flange. Electroplating the blank both creates the vaporbarrier and encapsulates the sulfur in the electroless copper coating,which has a high vapor pressure. Other methods can be used to coat thecomponents including, but not limited to, sputter deposition,sublimation, and chemical vapor deposition to name a few. Hydrophobic oroleophobic material may also be deposited to reduce pump down timewithout bakeout. Similarly, a chemically inactive material such asplatinum could be deposited in a highly reactive environment to reducethe effect of the sensors on a critical process. Insulating coatings,such as SiO₂ and Al₂O₃, can also be used as well. Additionally, maskingtechniques can be used to selectively coat portions of the component inorder to adjust its properties such as conductivity, outgassing, andsurface smoothness so that it is optimized for a particular vacuumapplication. Thus, coatings can be used to provide the desiredelectrical or mechanical properties. Incidentally, experimentation withsample blanks as shown in FIG. 7 is an excellent way to test polymermaterials and vapor barrier coatings against outgassing, permeation andmechanical properties.

Some vacuum seals, such as 2.75 inch ConFlat-type (NW35CF) and 1.33 inchConFlat-type (NW16CF), incorporate a knife edge or other raisedstructure designed to penetrate a gasket enhancing the performance ofthe seal. In a polymer seal constructed of a material with shape memoryproperties, such an elevated structure could be designed such that whenthe seal is clamped to a vacuum system the knife edge or raisedstructure would be slightly crushed so that it conforms to anyirregularities on the mating chamber side, increasing the integrity ofthe seal. When the component is taken off, and before re-use, heat canbe applied to the raised structure causing it to return to itspre-deformation shape prior to making a second seal. The shape memoryproperty can be exploited to assure the consistency of the seal whenused multiple times. FIG. 8 is an illustration of a vacuum blank 200having a body 210 formed of a polymer having shape memory properties.The vacuum blank 200 has a knife edge portion 220 for coupling to agasket or other structure. Other components and seals of a high vacuumhousing can also have a knife edge or other raised structure, asillustrated in FIG. 8.

The use of polymers to construct vacuum components also permits theconstruction of cathodes having different shapes, which may provide anadvantage in some instruments. For example, a cathode shaped like asection of a cone would have a natural self centering property.

One particular example of a polymer component is an ionization gauge,such as the cold cathode gauges 1000 illustrated in FIGS. 10-14. Theionization gauge has a cylindrical cathode cage 1010 having a base 1010a. The base 1010 a can have an opening 1010 b. A cathode pin 1015 can beelectrically coupled to the cylindrical cathode cage 1010. An anode 1020is disposed through the opening 1010 b of the base 1010 a of thecylindrical cathode cage 1010. An insulator 1025, shown in the shape ofa disc in the embodiment of FIG. 10, is preferably formed of a ceramic,such as an alumina ceramic, and protects the interior of the polymerhousing 1030 from plasma created during operation of a cold cathodecage. Typically, the insulator 1025 is located at the base 1010 a of thecylindrical cathode cage 1010. Tests results have shown that includingan insulator 1025 can result in significantly less deterioration of thepolymer housing. A polymer housing 1030 surrounds the cylindricalcathode cage 1010. A sputter shield 1035 can be disposed within thecylindrical cathode cage 1010 in order to reduce sputteringcontamination of the insulator 1025. The opening 1010 b of the base 1010a of the cold cathode cage 1010 can have a step edge 1010 e to shadowthe insulator 1025 to minimize contamination at the interface betweencathode 1010 and insulator 1025. A starter 1040 can be electricallycoupled to the anode 1020, disposed within the cylindrical cathode cage1010, and coaxial with the anode 1020. The starter 1040 can be press fitonto to the anode 1020, or it can be integrally formed with the anode1020. The use of such a starter location is preferred in extended rangegauges where fast turn-on times are required at the transition pressurefrom a Pirani gauge to a cold cathode gauge. Under such circumstances,the start is accelerated as a corona discharge is established betweenthe anode and the screen 1045 or cathode cage 1010.

A bottom face of the base 1010 a of the cylindrical cathode cage 1010can have a lip 1010 c surrounding and centering the insulator 1025, andthe lip 1010 c and insulator 1025 can be epoxied to each other toprevent a “virtual leak.” An upper portion of the cold cathode cage 1010can have a lip 1010 d that extends radially outward from the coldcathode cage 1010 into the polymer housing 1030, which can help to lockthe cylindrical cathode cage 1010 axially into the polymer housing 1030and reduce the flux due to a “virtual leak” caused by air trapped in athin volume surrounding the cathode that is not readily accessible. Ascreen 1045, which may be ferromagnetic, can be coupled to an upperportion of the cold cathode cage 1010.

The polymer housing 1030 can have a flange portion 1030 a, which can beused to couple the ionization gauge to a chamber. A cylindrical magnet1050 surrounds at least a portion of the polymer housing 1030. Anoptional snap ring 1052 (FIG. 13) can be disposed adjacent to an end ofthe magnet 1050 to support the magnet and hold it tightly in place bothradially and axially. FIG. 14 illustrates an embodiment having a magnetthat is insert molded into the polymer. Thus, the embodiment of FIG. 14does not have a snap ring as the magnet is placed in the mold with thecathode cage, anode, insulator, and cathode pin. The magnet can becharged after the full assembly is completed.

An O-ring 1055 disposed around the anode 1020, and above the base 1010 aof the cylindrical cathode cage 1010, can be embedded within the polymerhousing to further aid in providing a vacuum seal. A cylindricalinsulator 1065 can surround a portion of the anode 1020 disposed throughthe PCB 1060 a. An enclosure 1070 can at least partially surround thepolymer housing 1030 and PCBs 1060 a-c. Printed circuit board 1060 a isdisposed adjacent to an optional insulator 1057. In some instances, theenclosure 1070 is formed of a polymer. In some embodiments, a connector1075 can be coupled to the enclosure 1070. Polymer material has beenremoved 1080, for example by coring out, at the base of the polymerhousing 1030 b. The coring 1080 provides a more uniform wall thicknessto eliminate sink and poor cosmetics.

In some embodiments, one or more printed circuit boards (PCB) 1060 a-ccan be included. The anode 1020 is disposed through a first PCB 1060 a,and the polymer housing 1030 is mechanically coupled to the PCB 1060 a,typically by one or more fastening devices 1063 (e.g., screws). The PCBs1060 a-c can be joined by a PCB connector 1085.

A variety of flange configurations can be created for connecting a gaugeto a process chamber. FIG. 16A illustrates a standard flange. FIG. 16Billustrates a flange having an insert molded centering ring 1031. Inthis embodiment, the centering ring is metallic and overmolded into thepolymer housing. An O-ring can be added to couple to the housing to aprocess chamber. FIG. 16C is a one piece flange and centering ring 1032.In this embodiment the centering ring is polymer and molded as ahomogenous part of the polymer housing.

A housing for use in an ionization gauge can be made by positioning anionization gauge assembly within a mold, as illustrated in FIGS. 17A and17B. The ionization gauge assembly can include a cylindrical cathodecage 1010 having a base 1010 a and an opening 1010 b therein, a cathodepin 1015 electrically coupled to the cathode, an anode 1020 disposedthrough the opening 1010 b of the base 1010 a of the cylindrical cathodecage 1010, and an insulator 1025 at the base 1010 a of the cylindricalcathode cage 1010 configured to protect a polymer housing at aninterface between the cylindrical cathode cage 1010 and the polymerhousing. Molten polymer is then flowed into the mold and allowed tosolidify to form a housing 1030 around the cylindrical cathode cage,cathode pin, anode, and insulator. A cylindrical magnet 1050 can bepositioned so that it surrounds at least a portion of the polymerhousing 1030. An O-ring 1055 can be positioned around the anode 1020,within the polymer housing 1030, and above (as viewed in FIGS. 11-14)the base 1010 a of the cylindrical cathode cage 1010. One or more PCBs1060 a-c can be mechanically coupled to the polymer housing 1030, andthe anode 1020 can be disposed through one or more of the PCBs 1060 a-c.An enclosure 1070 can be positioned so that it surrounds the polymerhousing 1030 and the one or more PCBs 1060 a-c. A connector 1075 can becoupled to the enclosure 1070.

In essence, this process allows preassembly of the gauge sensorcomponents and then uses plastic injection molding to encapsulate thesensor elements into a housing in a single step, including vacuumsealing feedthroughs to the housing and providing an integrated mountingflange. The same methodology is applicable to other kinds of vacuumgauges, including ionization, thermal conductivity, and membranedeflection gauges. Using polymeric materials to develop and manufacturethe building blocks of vacuum gauges also allows production of lowercost gauges in which a combination of sensor technologies is combined toprovide an expanded measurement range. During operation, vacuum systemscan experience very wide pressure swings, and often multiple gauges areused to be able to provide measurements over the entire range ofoperation. Even though some of the gauges may not be used to measure thelowest vacuum levels, all of them need to compatible with operation athigh vacuum levels. The plastic material selections should take intoaccount not only the pressure measurement range of the gauge, but alsothe minimum pressure range to which the gauge will be exposed.

Another embodiment, which has an extended cold cathode cage, isillustrated in FIG. 15. Cathode cage 1110 a is extended downwardlytowards flange portion 1130 a of polymer housing 1130. One benefit ofthis arrangement is that the metal cathode lines a greater portion ofthe interior surface, preferably the entirety of the interior surface,of polymer housing 1130, which can reduce permeation of air andoutgassing from the polymer into a vacuum chamber.

The embodiments described herein incorporate a number of the features,or building blocks, for the design of gauges and sensors. Combiningthose building blocks into a single embodiment can create a particularlysuccessful gauge. For example, a gauge that includes a properly selectedpolymer material (e.g., not hygroscopic, provides low outgassing, hightensile strength and flexural modulus, and high dielectric strength)preserves the quality of the vacuum. Further inclusion of an electricalfeedthrough pin having a tortuous, or non-linear, path provides for alonger path length for gas molecules to traverse, thereby reducing gasflux from an air side to a vacuum side, which further improves thequality of the vacuum seal. Improving the quality of the vacuum sealcan, in turn, improve the sensitivity and accuracy of the resultinggauge measurements.

Typically, ionization gauges includes numerous other components, such asthose described in U.S. Patent Publication No. 2015/0091579, PCTPublication No. WO/2015/048664, and U.S. Pat. No. 7,847,559, theentirety of all of which are incorporated herein by reference. Thisapplication also incorporates herein by reference the entirety of U.S.Provisional Patent Application No. 62/103,968, filed on Jan. 15, 2015.

While this invention has been particularly shown and described withreferences to example embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

What is claimed is:
 1. A method of making a gauge, the methodcomprising: a) positioning a gauge assembly within a mold, the gaugeassembly comprising an electrical feedthrough pin disposed through anopening of a base; b) flowing molten polymer into the mold; and c)allowing the molten polymer to solidify to form a polymer vacuum housingaround the electrical feedthrough pin such that the electricalfeedthrough pin is disposed directly through the polymer vacuum housing.2. The method of claim 1, further comprising another electricalfeedthrough pin that is disposed through a side of the polymer vacuumhousing.
 3. The method of claim 1, wherein the electrical feedthroughpin has a nonlinear portion.
 4. The method of claim 3, wherein thenonlinear portion is disposed through the polymer vacuum housing.
 5. Themethod of claim 1, wherein the electrical feedthrough pin has a threadedportion disposed through the polymer vacuum housing.
 6. The method ofclaim 1, wherein the electrical feedthrough pin is further coupled tothe polymer vacuum housing with an O-ring. The method of claim 1,wherein the electrical feedthrough pin has an extended disc portiondisposed within the polymer vacuum housing.
 8. The method of claim 1,wherein the mold forms a flange to couple the gauge to a processchamber.
 9. The method of claim 1, wherein: the electrical feedthroughpin is an anode disposed through the opening of the base; and the gaugeassembly further comprises a cathode feedthrough pin that iselectrically coupled to a cylindrical cathode cage, wherein thecylindrical cathode cage comprises the base.
 10. The method of claim 9,wherein the gauge assembly further comprises a sputter shield disposedwithin the cylindrical cathode cage that is coaxial with the anode. 11.The method of claim 9, wherein the gauge assembly further comprises astarter that is electrically coupled to the anode and disposed withinthe cylindrical cathode cage.
 12. The method of claim 9, wherein anupper portion of the cylindrical cathode cage has a lip that extendsradially outward from the cylindrical cathode cage into the polymerhousing.
 13. The method of claim 9, wherein the gauge assembly furthercomprises a ferromagnetic screen coupled to an upper portion of thecylindrical cathode cage.
 14. The method of claim 9, further comprisingpositioning an O-ring around the anode, within the polymer housing, andbelow the base of the cylindrical cathode cage.
 15. The method of claim9, further comprising mechanically coupling a printed circuit board tothe polymer housing, wherein the anode is disposed through the printedcircuit board.
 16. The method of claim 9, wherein the polymer housing isformed of polyether ether ketone (PEEK), polypropylene, orpolycarbonate.
 17. The method of claim 9, wherein the polymer housing isformed of a polymer having an outgassing rate less than 5×10⁻⁶ Torr Ls⁻¹ cm⁻².
 18. The method of claim 9, wherein the polymer housing isformed of a polymer that is not hygroscopic.
 19. The method of claim 9,further comprising positioning a cylindrical insulator that surrounds aportion of the anode disposed through the printed circuit board.
 20. Themethod of claim 9, further comprising positioning an enclosure that atleast partially surrounds the polymer housing and printed circuit board.21. The method of claim 20, wherein the enclosure is formed of apolymer.
 22. The method of claim 20, further comprising coupling aconnector to the enclosure.